Milling Shaping and Planning.pdf .

Department of Mechanical & Manufacturing Engineering, MIT, Manipal 1 of 39
MANUFACTURING TECHNOLOGY
CHAPTER 6
MILLING, SHAPING & PLANING

Milling Machine

Metal is removed by moving the work piece against
the rotating multipoint cutting tool. Milling cutter is
mounted on a rotating spindle called arbor. Cutter
rotates at required cutting speed and work piece is
fed slowly past the milling cutter.
Milling machine

Main parts of the
Milling Machine
Base
Column
Knee

Table
Over hanging arm
Saddle
Main parts of the
Milling Machine

Spindle
Arbor
Main parts of the
Milling Machine

Types of Milling Machines
(a) Column and knee type milling machines
1. Hand miller
2. Plain milling machine
3. Universal milling machine
4. Vertical milling machine
5. Omniversal milling machine
(b) Fixed bed type milling machine
1. Simplex milling machine
2. Duplex milling machine
3. Triplex milling machine
(c) Planer milling machines

Types of Milling Machines
(d) Special type milling machines
1. Rotary table milling machine
2. Drum milling machine
3. Planetary milling machine
4. Pantograph profiling and tracer controlled milling
machine

2 structural elements, namely a COLUMN and a
KNEE.
Column contains spindle and drive mechanism &
knee moves vertically on the column.
Column and knee type milling
machines

A table travels longitudinally on the saddle and the
saddle travels transversely.
Column and knee type milling
machines

Plain Milling Cutters
❑ They have cylindrical shapes with teeth on their
circumference
❑ Central portion is hollow for holding in the arbor
❑ Straight milling cutters are used for producing flat
surfaces
❑ Helical milling cutters are used for profile milling
❑ Both are suitable for light and heavy duty
applications

Milling attachments

Milling operations

Indexing (Dividing)
Head
Used to divide circumference of work piece into
equally spaced divisions when milling gear teeth,
squares, hexagons, and octagons.
Universal Dividing Head
It is the most popular and common type of indexing
arrangement. As indicated by its name “universal”,
it can be used to do all types of indexing on a
milling machine. Universal dividing head can set
the work piece in vertical, horizontal, or in inclined
position relative to the worktable

Headstock with index plates
Headstock change gears
Universal chuck
Footstock
Center rest

The worm gear has 40 teeth and the worm has
simple thread. Crank is directly attached with the
worm. If we rotate the crank by 40 revolutions the
spindle attached with worm gear will revolve by only
one revolution and one complete turn of the crank
will revolve the spindle only by 1/40th
revolution
(turn).

In order to turn the crank precisely a fraction of a
revolution, an indexing plate is used. An indexing
plate is like a circular disc having concentric rings of
different number of equally spaced holes. Normally
indexing plate is kept stationary by a lock pin. A
spring loaded pin is fixed to the crank which can be
fixed into any hole of indexing plate. The turning
movement of the work piece is controlled by the
movement of crank.

Methods of Indexing
1. Direct indexing
2. Simple indexing
3. Angular indexing
3. Compound indexing
4. Differential indexing

• Simplest form of indexing
• Performed by disengaging worm shaft from worm
wheel by means of eccentric device in dividing head
• Used for quick indexing of work piece when cutting
flutes, hexagons, squares, etc.
• Direct indexing plate usually contains three sets of
hole circles or slots: 24, 30, and 36
1. Direct indexing
Methods of Indexing

Slots Direct indexing divisions
24 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __
30 2 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __
36 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36
1. Direct indexing

What direct indexing is necessary to mill eight flutes
on a reamer blank?
Slots Direct indexing divisions
24 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __
30 2 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __
36 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36
Since the 24-hole circle is the only one divisible by
8 (the required number of divisions), it is the only
circle that can be used in this case.
Never count the hole or slot in which
the index pin is engaged.
1. Direct indexing

What direct indexing is necessary to mill eight flutes
on a reamer blank?
If we want to divide the
surface into N parts then
number of holes by which pin
has to move (24 / N)
For N= 8 , 24/8 = 3.
i.e. after completing one pair of
milling whole surface of the work
piece has to be moved by 3 holes
before next milling operation, that is
to be done for 7 number of times.
1. Direct indexing

2. Simple indexing
It is also named as plain indexing. It over comes the
major limitation of direct indexing that is possibility of
dividing circumference of work piece into some fixed
Milling number of divisions.
In this case worm and worm gear is first engaged. So
one complete turn of indexing crank revolves the
work piece by 1/40th revolution.
Three indexing plates are used. These plates have concentric
circles of holes with their different numbers as described
below.

• Divide 40 by the number of divisions to be done on the
circumference of work piece. This gives movement of
indexing crank. Indexing crank movement 40/ N
N is the number of divisions to be made on the circumference of work piece.
• If the number is a whole number, then crank is rotated by
that much number of revolutions after each milling
operations, till the completion of the work.
• If indexing crank movement calculated by 40/ N is not
whole number, it is simplified and then expressed as a
whole number and a fraction. 40N
• The fractional part of the above number is further processed
by multiplying its denominator and numerator by a suitable
common number so that the denominator will turn to a
number equal to any number of holes available on the any
of indexing plates.

1 . Index for 8 divisions = 5
2 . Index for 30 divisions = 40/ 30 = 1 10/30
3 . Index for 136 divisions
Limitations
This method can be used for indexing up to 50, for any
number of divisions after 50 this method is not capable for
some numbers like 96, etc. Compound indexing
overcomes the limitations.

When the number of divisions required on the job is
outside the range of simple indexing (69, 57…..)
The word compound indexing is an indicative of
compound movements of indexing crank and then
plate along with crank.
3. Compound indexing

Operation carried by providing 2 separate simple
indexing movements.
1. Indexing plate is held stationary by a lock pin, and
the indexing crank rotated through a required
number of holes in a selected hole circle.
2. Crank is fixed through pin and followed by another
movement by disengaging the rear lock pin, the
indexing plate along with indexing crank is rotated
in forward or backward direction through
predetermined holes in a selected hole circle, then
lock pin is reengaged.

Suppose 69 divisions were required. In order to index
the work 1/69 revolution, it is necessary move the
crank 40/ 69 of a turn and this would require a circle
having 69 holes, if the simple method of indexing
were employed, but by the compound system, this
division can be obtained by using the 23- and 33-hole
circles
(21/ 23) - (11/33) = (40/69)

• The crank is first moved to the right 21 holes in the
23-hole circle.
• Then the rear lock pin is removed and crank
engaged with the 33-hole circle of the index plate.
• The plate is turned backward, or to the left, 11
holes in the 33-hole circle.
• This rotation of the plate also carries the crank to
the left.

Initial
position
2nd
position
3rd
position
21/ 23 movement - 11/33 movement
21 holes
4th
position

Example 1: 69 divisions of work piece circumference
by indexing method. (Using compound indexing)
(a) Factor the divisions to be make (69 = 3 x 23) N =
69.
(b) Select two hole circles at random (These are 27
and 33 in this case, both of the hole circles should be
from same plate).
Procedure
For selecting hole circle, use the expression [ N (a-b)]/ (40 a*b)
Where a & b are the two hole circles having number of holes ‘a’ & ‘b’. If the
numerator comes out to be unity, then the hole circle selected are correct.

1. Subtract smaller number of holes from larger
number and factor it as (33 – 23 = 10 = 2 x 5).
2. Factor the number of turns of the crank
required for one revolution of the spindle (40).
Also factorize the selected hole circles
Above selected holes, numerator is not unity. Hence
selected hole circles are not correct. Hence reselect
hole circle 23 and 33.

3. Place the factors of N and difference above the
horizontal line and factors of 40 and selected both the
hole circles below the horizontal line as given below.
Cancel the common values.
Multiply all the remaining factors below the line as:
2 x 2 x 11 =44
This indicates 44 holes to be crossed for
indexing.

Following formula is used for indexing
In this formula N1
= 23 and N2
= 33 and
n1
= number of holes to be moved
i.e.
For indexing of 69 divisions, the indexing crank should
be moved by 21 holes circle in forward direction and
then crank along with the plate are moved by 11 holes
in 33 hole circle is reversed (backward) direction.

Example 2 : 57 divisions of work piece circumference
by indexing method. (Using compound indexing)
[40/57] = [6/18]+ [7/19]

SHAPING AND PLANING

SHAPERS

Shaper
⚫ It is machine tool which produces flat surfaces.
⚫ They employ single point cutting tool.
⚫ The cutting tool is subjected to interrupted cuts; the
tool cuts in the forward stroke and is idle in the
return stroke.

Shaper – Working Principle

Planer
⚫ It is machine tool used to produce flat surfaces.
⚫ They employ single point cutting tool which is
stationary.
⚫ The table reciprocates in the guideways.
⚫ Accommodates large and heavy workpieces unlike
shaper.

Comparison: Shaper & Planer
⚫ The planer is used for large work, whereas, the
shape is used for smaller work.
⚫ On a planer the work is moved against a stationary
tool whereas, on the shaper the tool moves across
the stationary work.
⚫ On a planer the tool is fed into the work whereas, on
the shaper the work is fed across the tool.

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